At present, with regard to mobile communication technology, work is underway on standardizing LTE-A (LTE-Advanced), which is an advanced standard of the LTE (Long-Term Evolution: 3rd Generation) in the 3GPP (3rd Generation Partnership Project). Whereas in LTE communication is performed between a base station apparatus and a mobile station apparatus on a one-to-one basis, technology known as CoMP (coordinated multiple-point transmission and reception), which performs communication with a mobile station apparatus by a plurality of base station apparatuses sharing information and cooperating is being investigated, is expected to have the effect of improving the user throughput and cell throughput at the edge of a cell in comparison with LTE (refer to Non-Patent Reference 1).
With regard to CoMP, investigations are being done with regard to both the uplink and the downlink. In downlink CoMP, there are two general methods that are being investigated. One is a method in which, although one-to-one communication is performed with the base station apparatuses the same as in LTE, scheduling and beam forming cooperation is done by a plurality of adjacent base station apparatuses sharing information, thereby reducing interference. The other is a method in which, in contrast to LTE, simultaneous data transmission is done to one mobile station apparatus by a plurality of base station apparatuses, these data being linked and demodulated at the mobile station apparatus to improve quality. With regard to uplink CoMP, a method is being investigated whereby a plurality of base station apparatuses receive a signal from a mobile station apparatus and link these to improve quality.
The physical layers in LTE and LTE-A will now be described. In the physical layer, the physical channels and physical signal are defined. Six types of downlink physical channels are defined, these being:
PDSCH (Physical Downlink Shared Channel);
PBCH (Physical Broadcast Channel);
PMCH (Physical Multicast Channel);
PCFICH (Physical Control Format Indicator Channel);
PDCCH (Physical Downlink Control Channel); and
PHICH (Physical Hybrid ARQ Indicator Channel).
Two types of downlink physical signals are defined, these being:
RS (Reference Signal) and
SS (Synchronization Signal).
Three types of uplink physical channels are defined, these being:
PUSCH (Physical Uplink Shared Channel);
PUCCH (Physical Uplink Control Channel); and
PRACH (Physical Random Access Channel).
Only one type of uplink physical signal is defined, this being RS (Reference Signal).
PDSCH and PUSCH are physical channels used mainly for transmitting user data and control data. PBCH is a physical channel for transmitting notification information. PMCH is a physical channel for transmitting multicast data of broadcasts and the like. PCFICH is a physical channel for notification of the number of PDCCH symbols. PDCCH is a physical channel for transmitting commands and the like for PDSCH and PUSCH scheduling and TPC (Transmit Power Control). PHICH is a physical channel for transmitting an ACK/NACK of an HARQ (Hybrid ARQ (Automatic Repeat Request)) with respect to the PUSCH.
PUCCH is a physical channel for transmitting an ACK/NACK of an HARQ with respect to PDSCH, CQI (Channel Quality Information), PMI (Precoding Matrix Indication), RI (Rank Indication) and the like. PRACH is a physical channel for transmitting a random-access preamble. The uplink and downlink RS is defined as a physical signal used in channel prediction and the measurement of the CQI, and SS is defined as a physical signal used for cell searching.
In mobile communication technology, when a disconnect occurs during communication between a mobile station apparatus and a base station apparatus, re-connection is done. Because it is desirable that the time required for this re-connection be further shortened, it is necessary for the mobile station apparatus to select the base station apparatus that is to be the re-connection destination and to complete re-connection processing more quickly. Re-connection processing will be described below. FIG. 12 shows an example of the positional relationships between a mobile station apparatus and base station apparatuses in a conventional mobile communication system. The mobile station apparatus A is positioned at the edge of the cell A of the base station apparatus A, and communicates with the base station apparatus A. In the case in which the signal quality deteriorates during communication between the mobile station apparatus A and the base station apparatus A and a disconnect occurs, the mobile station apparatus A performs a band search and measures the received level of RS (Reference Signal), the path loss, and the SNR (signal-to-noise ratio) and the like, which are the quality of the signals of the nearby base station apparatuses A, B, and C. There are cases in which, as noted in Non-Patent Reference 2, the RSRP (Reference Signal Received Power), which indicates the average received power of the reference signal, is measured.
As a result of this measurement, the mobile station apparatus A takes a base station apparatus having good signal quality that is at least a certain level as a re-connection destination base station apparatus candidates, and selects the re-connection destination from these candidates. In this case, if the base station apparatus B is selected, the mobile station apparatus A sends a random-access signal to the base station apparatus B for the purpose of establishing synchronization with the base station apparatus B, and performs random-access processing. In the random-access processing, the transmission timing from the mobile station apparatus A is adjusted, and notification is made by the base station apparatus B to the mobile station apparatus A of information regarding the transmission timing. After that, the mobile station apparatus A, based on this information, begins communication with the base station apparatus B.
In Patent Reference 1, art is proposed in which, by making a selection that excludes a base station apparatus that has been disconnected, the time required for a band search is reduced.